The present invention relates to coil springs and, more particularly, to coil springs for use within a brake cylinder.
Automobile braking systems incorporating drum brakes typically include a master cylinder and a slave cylinder wherein the master cylinder is used to actuate the slave cylinder located within a brake drum assembly. The slave cylinder includes a pair of opposing pistons located adjacent to opposing ends of the cylinder and a seal is located behind each of the pistons to prevent fluid from leaking out of the cylinder through the clearance area between the pistons and the cylinder walls. The outer end of each of the pistons is adapted to engage an end of a brake shoe such that actuation of the pistons results in the brake shoes being biased outwardly into firm engagement with the brake drum.
In order to ensure that the seals behind the pistons remain separated from each other and remain positively engaged with the pistons and the inner wall of the cylinder, the slave cylinder is also provided with a spring located between the opposing pistons and engaged within a frustoconical-shaped recess on the seals. The spring is formed having the shape of a cylindrical helix and, in order to provide a proper bearing surface for engaging the recesses in the seals, a pair of frustoconical-shaped sheet metal rings or caps are attached to the ends of the spring by means of staking. This spring is relatively expensive to produce since it requires separate operations for forming the spring and the metal rings, as well as for attaching the rings to the ends of the spring. Further, this constructions is subject to failure if the rings separate from the spring at the staking points, which failure could result in the internal bore of the cylinder becoming scraped as the rings move around relative to the spring and thus requiring reworking or replacement of the slave cylinder.
Accordingly, there is a need for a spring for use within a brake cylinder which is economical to produce and which is not subject to failure as a result of the end portions separating from the spring.